Directional drilling can be described as the intentional deviation of a wellbore from the path it would naturally take. This is accomplished through the use of whipstocks, bottomhole assembly (BHA) configurations, instruments to measure the path of the wellbore in three-dimensional space, data links to communicate measurements taken downhole to the surface, mud motors and special BHA components and drill bits. In some cases, such as drilling steeply dipping formations or unpredictable deviation in conventional drilling operations, directional-drilling techniques may be employed to ensure that the hole is drilled vertically.
The most common way to directional drill is through the use of a bend near the bit in a downhole steerable mud motor. Directional drilling is accomplished with the alternating combination of two drilling operations. In the sliding mode the drill string is slowly rotated to orient the bend in the desired direction so that the bend points the bit in a direction different from the axis of the wellbore. Once oriented by pumping mud through the mud motor, the bit turns while the drill string does not rotate but rather slides, allowing the bit to drill in the direction it points. When a particular wellbore direction is achieved, that direction may be maintained by rotating the entire drill string so that the bit does not drill in a single direction off the wellbore axis, but instead sweeps around and its net direction coincides with the existing wellbore.
In directional drilling operations the sliding phase of drilling lacks the efficiency associated with rotating the drill string. This inefficiency is a result of the drag of the sliding drill string along the borehole and the sole use of the mud motor for drilling the borehole.
In recent years the industry has seen the development of rotary steerable systems for used in directional drilling. These systems employ the use of specialized downhole equipment to replace conventional directional tools such as mud motors. A rotary steerable tool is designed to drill directionally with continuous rotation of the drill string from the surface, eliminating the need to slide a steerable mud motor. Continuous rotation of the drill string allows for improved transportation of drilled cuttings to the surface resulting in better hydraulic performance and reduced well bore tortuosity due to utilizing a steadier steering model. Rotary steerable systems are costly as compared to mud motor systems, so more the traditional mud motor systems are more economically preferable in conventional directional drilling applications.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.